Abstract: This invention provides an improved “blow off valve” for use on turbocharged engines. The valve is of a new style having a main body which is comprised of a tube which can be incorporated into the charge air plumbing of a turbocharged engine. The tube is perforated around its circumference creating ports through which the pressurized air from a turbocharger can escape. The ports are covered during normal running conditions by an annular sleeve which fits over the main tube body. The sleeve is able to slide back and forth along the main body tube and in doing so it can alternately cover or uncover the ports in the main body. The sleeve is constructed in such a way that it acts as a pneumatic piston and is moved back and forth by alternate conditions of vacuum or positive pressure that are applied to it.